In this variation on a standard cold foam mixing method, the whole eggs are separated and beaten separately into two foams. These foams are then folded together. The separated foam mixing method is slightly more difficult than the cold foaming method because the egg whites, which are whipped alone, can rapidly lose volume. For this reason it is important when using this mixing method that all ingredients and equipment are assembled and receive any preliminary treatment before you begin to mix the batter (e.g., line pans, sift dry ingredients, melt fat, etc.). Dry ingredients should be sifted for aeration as well as to eliminate any lumps that may require extra mixing as dry ingredients are incorporated into the delicate aerated egg mixture.